The present invention relates generally to spoolable tubing suitable for use in the oil industry, and more particularly to spoolable tubing consisting of a composite material with the ability to withstand high stress.
Spoolable tubing, that is tubing capable of being spooled upon a reel, is commonly used in numerous oil well operations. Typical oil well operations include running wire line cable down hole with well tools, working over wells by delivering various chemicals down hole, and performing operations on the interior surface of the drill hole. The tubes used are required to be spoolable so that the tube can be used in conjunction with one well and then transported on a reel to another well location. Steel coiled tubing is typically capable of being spooled because the steel used in the product exhibits high ductility (i.e. the ability to plastically deform). Unfortunately, the repeated spooling and use of steel coiled tubing causes fatigue damage that can suddenly cause the steel coiled tubing to fracture and fail. The hazards of operating steel coiled tubing, i.e. risk to personnel and high economic cost resulting from down time needed to retrieve the broken tubing sections, forces steel coiled tubing to be retired after a relatively few number of trips into a well.
Steel coiled tubing has also proven to be subject to expansion after repeated uses. Tube expansion results in reduced wall thickness with the associated reduction in the pressure carrying capability of the steel coiled tubing. Steel coiled tubing known in the art is typically limited to an internal pressure up to about 5,000 psi. Accordingly, higher pressure and continuous flexing typically reduces the steel tube""s integrity and service life.
For example, the present accepted industry standard for steel coiled tube is an A-606 type 4 modified HSLA steel with yield strengths ranging from 70 ksi to 80 ksi. The HSLA steel tubing typically undergoes bending, during the deployment and retrieval of the tubing, over radii significantly less than the minimum bending radii needed for the material to remain in an elastic state. The repeated bending of steel coiled tubing into and out of plastic deformation induces irreparable damage to the steel tube body leading to low-cycle fatigue failure.
Additionally, when steel coiled tubing is exposed to high internal pressures and bending loads, the isotropic steel is subjected to high triaxial stresses imposed by the added pressure and bending loads. The high triaxial stresses result in significant plastic deformation of the tube and diametral growth of the tube body, commonly referred to as xe2x80x9cballooningxe2x80x9d. When the steel coiled tube experiences ballooning, the average wall thickness of the tube is reduced, and often causes a bursting of the steel tube in the area of decreased thickness.
Steel coiled tubes also experience thinning of the tube walls due to the corrosive effect of materials used in the process of working over the well and due to materials located on the inner surface of the well bore. The thinning resulting from corrosive effects of various materials causes a decrease in the pressure and the tensile load rating of the steel coiled tubing.
It is, therefore, desirable to provide a non-steel coil tubing which is capable of being deployed and spooled under borehole conditions, which does not suffer from the limitations of steel tubing and is highly resistant to chemicals.
For the most part, prior art non-metallic tubular structures that are designed for being spooled and also for transporting fluids, are made as a hose whether or not they are called a hose. An example of such a hose is the Feucht structure in U.S. Pat. No. 3,856,052 which has longitudinal reinforcement in the side walls to permit a flexible hose to collapse preferentially in one plane. However, the structure is a classic hose with vulcanized polyester cord plies which are not capable of carrying compression loads or high external pressure loads. Hoses typically use an elastomer such as rubber to hold fiber together but do not use a high modulus plastic binder such as epoxy. Hoses are designed to bend and carry internal pressure but are not normally subjected to external pressure or high axial compression or tension loads.
When the ends of a hose are subjected to opposing forces, the hose is said to be under tension. The tensile stress at any particular cross-section of the hose is defined as the ratio of the force exerted on that section by opposing forces to the cross-sectional area of the hose. The stress is called a tensile stress, meaning that each portion pulls on the other.
With further reference to a hose subjected to opposing forces, the term strain refers to the relative change in dimensions or shape of the hose that is subjected to stress. For instance, when a hose is subjected to opposing forces, a hose whose natural length is L0 will elongate to a length L1=L0+Delta L, where Delta L is the change in the length of the hose caused by opposing forces. The tensile strain of the hose is then defined as the ration of Delta L to L0, i.e. the ratio of the increase in length to the natural length.
The stress required to produce a given strain depends on the nature of the material under stress. The ratio of stress to strain, or the stress per unit strain, is called an elastic modulus. The larger the elastic modulus, the greater the stress needed for a given strain.
For an elastomeric type material, such as used in hoses, the elongation at break is so high (typically greater than 400 percent) and the stress-strain response so highly nonlinear; it is common practice to define a modulus corresponding to a specified elongation. The modulus for an elastomeric material corresponding to 200 percent elongation typically ranges form 300 psi to 2000 psi. In comparison, the modulus of elasticity for typical plastic matrix material used in a composite tube is from 100,000 psi to 500,000 psi or greater, with representative strains to failure of from 2 percent to 10 percent. This large difference in modulus and strain to failure between rubber and plastics and thus between hoses and composite tubes is what permits a hose to be easily collapsed to an essentially flat condition under relatively low external pressure. This large difference also eliminates the hose""s capability to carry high axial tension or compression loads while the higher modulus characteristic of the plastic matrix material used in a composite tube is sufficiently stiff to transfer loads into the fibers and thus resist high external pressure and axial tension and compression without collapse.
The procedure to construct a composite tube to resist high external pressure and compressive loads involves using complex composite mechanics engineering principles to ensure that the tube has sufficient strength. It has not been previously considered feasible to build a truly composite tube capable of being bent to a relatively small diameter, and be capable of carrying internal pressure and high tension and compression loads in combination with high external pressure requirements. Specifically a hose will not sustain high compression and external pressure loads.
Accordingly, it is one object of this invention to provide an apparatus and method for providing a substantially non-ferrous spoolable tube that does not suffer from the structural limitations of steel tubing and that is capable of being deployed and spooled under bore hole conditions.
A further object of the invention is to provide a composite coiled tube capable of working over wells and delivering various chemicals down hole quickly and inexpensively.
Another object of the invention includes providing a coiled tubing capable of repeated spooling and bending without suffering fatigue sufficient to cause fracturing and failing of the coiled tube.
Other objects of the invention include providing a spoolable tube capable of carrying corrosive fluids without causing corrosion in the spoolable tube, providing a coiled tube having less weight, and providing a coiled tube capable of withstanding higher internal pressure levels and higher external pressure levels without loosing tube integrity.
These and other objects will be apparent from the description that follows.
The invention attains the foregoing objects by providing a composite coiled tube that offers the potential to exceed the performance limitations of isotropic metals currently used in forming coiled tubes, thereby increasing the service life of the coiled tube and extending the operational parameters of the coiled tube. The composite coiled tube of the invention overcomes the disadvantages in present steel coil tubing by providing, among other things, a composite layer that exhibits unique anistropic characteristics capable of providing improved burst and collapse pressures as well as improved tensile strength, compression load strength, and load carrying capability.
The composite coiled tube of the present invention comprises a composite layer having fibers embedded in a matrix and an inner liner formed from polymeric materials or metal. The fibers in the composite layer are oriented to resist internal and external pressure and provide low bending stiffness. The composite coiled tube offers the potential to exceed the performance limitations of isotropic metals, thereby increasing the service life of the tube and extending operational parameters. In addition, the fibers, the matrix, and the liner used in the composite coiled tube can make the tube impervious to corrosion and resistant to chemicals used in treatment of oil and gas wells or in flowlines.
The service life potential of the composite coiled tube constructed in accordance with the invention is substantially longer than that of conventional steel tube when subjected to multiple plastic deformation bending cycles with high internal pressures. Composite coiled tube also provides the ability to extend the vertical and horizontal reach of existing concentric well services. In one operation, the composite coiled tube is deployed as a continuous string of small diameter tubing into a well bore to perform a specific well bore procedure. When the service is completed, the small diameter tubing is retrieved from the well bore and spooled onto a large reel for transport to and from work locations. Additional applications of coiled composite tube are for drilling wells, flowlines, as well as for servicing extended reach applications such as remedial work in wells or flowlines.
In particular, the invention provides for a composite coiled tube having an inner liner and a composite layer enclosing the inner liner. The composite layer contains three fibers oriented in a triaxial braid. A triaxial braid structure is formed of three or more fibers braided in a particular orientation and embedded in a plastic matrix. In a triaxial braid, a first structural fiber helically or axially extends along the longitudinal axis of the tube. A second braiding fiber is clockwise helically oriented relative to the first structural fiber or relative to the longitudinal axis of the tube. A third braiding fiber is counter-clockwise helically oriented relative to the first structural fiber or relative to the longitudinal axis of the tube. In addition, the first structural fiber is interwoven with either the second or the third or both braiding fibers. The composite coiled tube constructed with this triaxial braid structure exhibits unique anistropic characteristics having enhanced burst pressure characteristics, collapse pressure characteristics, increased bending characteristics, tensile loads, and compression loads.
The composite layer can be constructed with a matrix material having a tensile modulus of at least 100,000 psi, a maximum tensile elongation of at least 5%, and a glass transition temperature of at least 180 Degrees Fahrenheit. Increased tube strength can also be obtained by forming a layer having at least 80%, by fiber volume, of the fibers helically oriented relative to the longitudinal axis of the tube at an angle between 30 and 70 degrees.
In accordance with further aspects of the invention, the composite tube includes a liner that serves as a pressure containment member to resist leakage of internal fluids from within the tubing. The inner liner can be formed of metal or co-extruded composite polymers. The polymers forming the liner can also include homo-polymers or co-polymers. The metal or polymeric material forming the liner are impermeable to fluids (i.e. gasses and liquids). The inner liner can also include materials that are chemically resistive to corrosives.
The liner provides a path for conducting fluids (i.e. liquids and gases) along the length of the composite tube. The liner can transmit fluids down hole for operations upon the interior surfaces of the well hole, or the liner can transmit fluids or gases to hydraulic or pneumatic machines operably coupled to the composite tube. That is, the liner can provide a conduit for powering and controlling hydraulic or pneumatic machines. The composite tube can have one liner or a plurality of liners for conducting fluids along the length of the composite tube.
The liner can be constructed to have improved mechanical properties that enhance the bending characteristics, the strength characteristics, and the pressure characteristics of the coiled composite tube. For example, the liner can have a mechanical elongation of at least 25%, and a melt temperature of at least 250 degrees Fahrenheit. The liner can also enhance the pressure characteristics of the composite tube by increasing the bonding strength between the inner liner and the composite layer. This can be achieved by placing groves on the exterior surface of the liner, such that the grooves can hold matrix material that binds the composite layer to the exterior of the liner.
Another feature of the invention includes providing a liner capable of dissipating static charge buildup. A liner having an additive of carbon black can prevent static charge buildup. By preventing static charge buildup, the liner is more likely to prevent the ignition of flammable fluid circulating within the tube.
In a preferred embodiment, the composite layer is formed of three or more fibers interwoven in a triaxial braid and suspended in a matrix material. For example, the composite layer can comprise a helically extending first fiber, a second fiber clockwise extending and helically oriented, and a third fiber counter clockwise extending and helically oriented. The first, second and third fibers are oriented such that the first fiber is interwoven with either the second fiber or the third fiber or both The composite layer can also include additional plies formed of fiber and matrix. The fibers in the additional plies can have fibers oriented in many ways, including but not limited to, triaxially braiding, biaxially braiding, interwoven and filament wound.
Additional aspects of the invention provide for a separate interface layer interposed between the liner and the composite layer. This interface layer allows the composite coiled tube to withstand extreme pressures inside and outside the tube without causing degradation of the composite tube. The interface layer bonds the composite layer to the liner. In addition, the interface layer can serve as a transition layer between the composite layer and the liner. For example, the interface layer can have a modulus of elasticity between the axial modulus of elasticity of the liner and the axial modulus of elasticity of the composite layer, thereby providing a smooth transition in the modulus of elasticity between the liner and the composite layer.
Other aspects of the invention include a composite coiled tube having a pressure barrier layer. The pressure barrier layer can be located external to the composite layer for preventing fluids (i.e. gases or liquids) from penetrating into the composite tube. The pressure barrier layer also prevents external pressure from being directly applied to the outer surface of the inner liner, thereby preventing exterior pressure from collapsing the inner liner. The pressure barrier layer can be formed of an impermeable material such as either polymeric film (including polyester), thermoplastic, thermoset film, elastomer or metallic film. The impermeable material can be helically or circumferentially wrapped around the composite layer. In addition, the pressure barrier layer can include a fused particle coating. Preferably, the pressure barrier layer has a minimal tensile elongation of 10% and an axial modulus of elasticity of less than 750,000 psi, to aid in the enhanced bending and pressure characteristics of the composite coiled tube.
Further features of the invention provide for a composite tube having an outer protective layer external to the composite layer. The outer protective layer can provide an outer protective surface and an outer wear resistant surface. The outer protective layer can also resist impacts and abrasion. In those aspects of the invention having both a pressure barrier layer and a outer protective layer, the pressure barrier layer is typically sandwiched between the composite layer and the outer protective layer.
An additional feature of the invention is an energy conductor embedded in the composite tube. The energy conductor extends along the length of the composite tube. Energy conductors include electrical medium (such as electrical wiring), optical medium (such as fiber optics), hydraulic medium (such as a fluid impermeable tube), and pneumatic medium (such as a gas impermeable tube). The energy conductors can be embedded within the liner or within the composite layer of the spoolable composite tube.
Energy conductors commonly have low strain capability and thus can be damaged easily by large deformations such as those imposed by bending. These energy conductors are thus oriented in a helical direction relative to the longitudinal axis of the tube. This orientation minimizes the strain on the energy conductor when the tube bends. In an alternative aspect of the invention, the energy conductors can be aligned axially along the length of the tube. Two axially aligned energy conductors that are diametrically opposed along the length of the tube can provide a bending moment along the length of the composite tube, such that the conductors are located on a neutral bending axis that minimizes bending strains on the conductors.
Various embodiments of the invention exist which include one or more aspects and features of the invention described above. In one embodiment, the spoolable composite tube comprises an inner liner and an outer composite layer. In all embodiments, the tube can be designed to include or exclude an interface layer sandwiched between the inner liner and the composite layer. The interface layer increases the bonding strength between the liner and the composite layer. Other embodiments provide for a composite tube including a liner, a composite layer, and a pressure barrier. Further embodiments include a liner, a composite layer, a pressure barrier, and an external protective layer. While in an additional embodiment, the composite tube might include only a liner, a composite layer, and a pressure barrier. The invention also contemplates a spoolable tube having a liner, an inner composite layer, a pressure barrier, and an outer composite layer surrounding the pressure barrier.